Add stubs and glue for routing a request for an image from the clipboard.

ui/base/clipboard/clipboard.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_BASE_CLIPBOARD_CLIPBOARD_H_
 #define UI_BASE_CLIPBOARD_CLIPBOARD_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 130 matching lines @@
 
   // Reads UNICODE text from the clipboard, if available.
   void ReadText(Buffer buffer, string16* result) const;
 
   // Reads ASCII text from the clipboard, if available.
   void ReadAsciiText(Buffer buffer, std::string* result) const;
 
   // Reads HTML from the clipboard, if available.
   void ReadHTML(Buffer buffer, string16* markup, std::string* src_url) const;
 
+  // Reads an image from the clipboard, if available. The returned data will be
+  // encoded in PNG format.
+  void ReadImage(Buffer buffer, std::string* data) const;
+
   // Reads a bookmark from the clipboard, if available.
   void ReadBookmark(string16* title, std::string* url) const;
 
   // Reads a file or group of files from the clipboard, if available, into the
   // out parameter.
   void ReadFile(FilePath* file) const;
   void ReadFiles(std::vector<FilePath>* files) const;
 
   // Reads raw data from the clipboard with the given format type. Stores result
   // as a byte vector.
@@ skipping 106 matching lines @@
   GtkClipboard* clipboard_;
   GtkClipboard* primary_selection_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(Clipboard);
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_CLIPBOARD_CLIPBOARD_H_